CodeBurner for Firebug : CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.

CookieSwap : CookieSwap enables you to easily swap all your cookies so that you can be logged in to multiple web e-mail accounts (like Gmail and Yahoo! mail) as different users at the same time and quickly switch between them.

Cooliris : The Cooliris 3D Wall — Simply the fastest and most stunning way to browse photos and videos from the Web or your desktop. Effortlessly scroll an infinite “3D Wall” of your content from Facebook, Google Images, YouTube, Flickr, and hundreds more.

Greasemonkey : Allows you to customize the way a webpage displays using small bits of JavaScript.

GTDInbox for Gmail : Use GTDInbox to effectively manage your inbox, reduce email overload and maintain inbox zero. Turn emails into actions, and Gmail into an easy to use task manager, to get things done.

MediaWrap : This sexy baby can transparently wrap ActiveX into the Plugins which supported by firefox. You can just link the media files(Wmplayer, Rmplayer, QtPlayer and FlashPlayer) as normally without security problems.

Page Speed : Page Speed is an open-source Firefox/Firebug Add-on. Webmasters and web developers can use Page Speed to evaluate the performance of their web pages and to get suggestions on how to improve them.

Pencil : Pencil is a Firefox add-on to do GUI prototyping and simple sketching

Personal Menu : “Menus Toolbar” item is now available in Toolbar Context Menu and you may hide it forever!

ReloadEvery : Reloads web pages every so many seconds or minutes. The function is accessible via the context menu (menu you get when you right click on a web page) or via a drop down menu on the reload button …

TinEye Reverse Image Search : TinEye is a reverse image search engine. The plugin adds a right-click menu item that allows you to search for an image to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution …

TooManyTabs : TooManyTabs allows you to store as many tabs as you like by adding extra rows in the Firefox! It saves your browser’s space and memory as idle tabs are put aside. The extra rows also help to better prioritize and visualize your tabs.